The present invention relates to a liquid crystal material and a liquid crystal display device using the same.
At the present time, a TN type display method of using TN (Twisted Nematic) liquid crystal is most of extensively used for a liquid display device. In recent years, several liquid crystal display modes using ferroelectric liquid crystal or antiferroelectric liquid crystal as a liquid crystal material have been examined in order to attain a faster response speed and a wider viewing angle than the TN liquid crystal.
In a liquid crystal display device using ferroelectric liquid crystal, a double refraction mode, a dichroism mode, and a light scattering mode are mentioned as a switching mode. Among them, a dichroism mode (guest-host method) using a liquid crystal material containing a dichroic dye is a preferable mode in consideration of light utilizing efficiency, since it can manage with one polarizer. However, a large tilt angle (about 45.degree.), suitable in the guest-host mode, is hard to attain in the temperature range (including room temperature) which is practically used. Because of this and some other problems, a ferroelectric liquid crystal which is suitable for a dichroism mode and which can serve to provide a high contrast ratio and a wide viewing angle has not been developed yet.
Also, a liquid crystal display device using ferroelectric liquid crystal has a problem that it is poor in shock resistivity.
In a liquid crystal display device in which antiferroelectric liquid crystal is used, it is desirable to subject the liquid crystal to symmetric driving in which the polarity of voltage applied to the liquid crystal is inverted every frame periods. This is because the symmetric driving serves to prevent display failure known as "burn" which may result from the electric charge accumulated in a limited part of the liquid crystal. However, there has been developed no antiferroelectric liquid crystal which has a large tilt angle (about 45.degree.) suitable for symmetric driving in the practical temperature range (including room temperature) and which can achieve high contrast and a wide viewing angle.